21609564 has 24 divisors (see below), whose sum is σ = 51596160. Its totient is φ = 7035504.

The previous prime is 21609559. The next prime is 21609571. The reversal of 21609564 is 46590612.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 20424 + ... + 21455.

It is an arithmetic number, because the mean of its divisors is an integer number (2149840).

Almost surely, 2^21609564 is an apocalyptic number.

It is an amenable number.

21609564 is an abundant number, since it is smaller than the sum of its proper divisors (29986596).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21609564 is a wasteful number, since it uses less digits than its factorization.

21609564 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41929 (or 41927 counting only the distinct ones).

The product of its (nonzero) digits is 12960, while the sum is 33.

The square root of 21609564 is about 4648.6088241537. The cubic root of 21609564 is about 278.5364277994.

The spelling of 21609564 in words is "twenty-one million, six hundred nine thousand, five hundred sixty-four".